the invention relates to a concentric tubular membrane device useful in carrying out ion exchange or absorbent processes.
Liquid streams often contain undesirable dissolved impurities or contaminants which may be removed by ion exchange or absorbent processes. For example, industrial wastewater effluents may contain metals such as copper, chromium, zinc, nickel, cadmium, and lead which environmental regulatory agencies mandate must be removed from industrial effluents prior to discharge. Wastewater or groundwater may require treatment due to contamination by various organic compounds such as halogenated hydrocarbons or pesticides which pose environmental or health hazards. Industrial process water may require purification prior to use because of the presence of compounds such as calcium and magnesium sulfates and bicarbonates which cause scaling and fouling of plant equipment such as boilers. Conventional ion exchange resins or absorbents such as activated carbon are frequently used to remove such impurities or contaminants from water.
Conventional equipment used for carrying out ion exchange or absorbent processes consists of large tanks containing ion exchange or absorbent particles of about 16 to about 50 mesh U.S. Sieve Series ASTM E-11-61 (about 1.2 to about 0.3 millimeters in diameter) supported on screens, beds of sand, or other porous material possessing smaller openings than the diameter of the particles. Ion exchange or absorbent bed depths of several feet are commonly used. The limiting kinetic step in such processes is usually the rate at which the absorbing compound can diffuse from the liquid to the surface of the ion exchange or absorbent particles and then into the particles themselves. Finer, that is, smaller, particle sizes allow the diffusion step to proceed more rapidly by reducing the distance through which the absorbing compounds must diffuse. However, as the particles are reduced in size, the pressure drop across such beds becomes impractically high.
What is needed is an ion exchange or absorbent device and process for treating large volumes of liquid containing metals and/or organics in which the bed depth of ion exchange or absorbent particles is reduced and the particle size is reduced, so that the pressure drop across the bed may be maintained at practical levels while increasing the diffusion rate of the absorbing compounds through the bed by reducing the particle size. Reduction in particle size requires a simultaneous increase in mesh number of the bed supporting surface to prevent loss of ion exchange or absorbent particles. Furthermore, it is desirable to protect the upper layer of a shallow particle bed from turbulence created by the liquid being treated in order to prevent physical disruption of bed uniformity which can cause undesirable channelling and uneven distribution of the liquid being treated through the bed.